Highlight model of echoes from sonar targets

I.IntroductionTheecho-rangingapproachistheonlycffectiveapproachfordetectionandidentifi-cationofunderwatertargetifitisasilcntobkct.Echoformationisaphysicalprocessinwhichthetargetisexcitcdbyincidentwavc.Byechothecharactcristicinformationsoftargethavebcencarricd.Suchinformationsarejustfundamentalsofdetectionandiden-hficationappliedbyactivesonars.Classificationandidentificationareimportantdevelopmentsofreccntsonarsin-c1udingthehomersoftorpedocs.Thisneedsadecpunderstandingrcferredtoechobe-haviors…     

声呐目标回波的亮点模型

本文为声呐工程提供一个实用的目标模型.基于大多数声呐系统采用高频限带信号的事实,用传递函数描述目标的回波特性比较适宜.在高频情况下,构成回波的各种成分,如镜反射波、棱角波和各种弹性散射波都可以等效成某个散射中心即亮点的回波.整个目标等效成一组空间分布亮点.本文给出亮点传递函数的普遍形式,它由幅度因子、时延和相位跳变三个参量描述.一个完整的目标模型就是给定这三个参量组、利用本文给出的亮点模型可以实现窄带回波波形的模拟.     

浅海小掠射角的海底界面声反向散射模型的简化

在浅海,尤其是负梯度声速剖面和海面较为平静的浅海波导,海底界面反向散射是浅海混响的主要来源.经验散射模型只适用于分析浅海混响平均强度衰减特性,而基于物理机理建立的反向散射模型克服了这一缺陷,但同时也引入了其受地声模型约束的问题.本文结合了海底反射系数的三参数模型,对浅海远场海底反向散射模型进行了简化,以减少地声模型的输入参数.理论分析了海底反射系数的相移参数可以描述海底对声场的散射作用,无需任何海底地声参数的先验知识.通过对海底反向散射模型近似简化,结果表明在临界角附近和甚小掠射角范围内的海底粗糙界面反向散射模型的角度特性和强度特性受海底沉积层的影响不同:在临界角附近,海底反向散射的角度特性受海底反射系数的相移参数加权,而其散射系数则近似与相移参数无关;对于甚小掠射角,海底反向散射的角度特性近似与海底反射系数的相移参数无关,其散射系数则近似与相移参数的4次方成正比.     

A fast estimation of sonar cross section of acoustically large and complex underwater targets using a deterministic scattering center model

In this paper, a fast method is proposed to estimate the sonar cross section of acoustically large and complex underwater targets such as submarines and torpedoes. The proposed method is based on a deterministic scattering center model which constructs scattering center database by using a combining method of physical optics and geometric optics and then reconstructs sonar cross section patterns from that database with a polynomial interpolation with respect to the incident angle. The parametric studies to find appropriate intervals of the reference incident angle are systematically carried out for simple targets such as a flat square plate and an orthogonal dihedral. Moreover, to validate the proposed method, sonar cross sections of real-like targets such as a pressure hull and an idealized submarine are calculated. The comparisons show that the results by the proposed method are in good agreement with those by the direct calculation.     

浅海混响的垂直相关和海底反射损失与散射强度的反演

根据浅海混响射线简正波理论和可分离的海底散射模型,导出了混响垂直相关的表达式,理论研究和实验结果表明垂直相关与接收深度有关,与声源深度无关。提出一种利用混响强度衰减曲线与混响垂直相关曲线联合反演海底反射损失和海底散射强度的方法。数值模拟反演及对实验数据的反演表明:所提出的反演方法具有实验简便、反演速度比较快及反演的结果比较稳定等特点。     

Propagation of quasi-periodic random sound pulse sequence signals in shallow-water waveguides

It is an efficient method to model ship radiated noise as quasi-periodic random sound pulse sequences.Based on the model,this paper discusses the characteristics change of ship noise after through shallow-water waveguides.Theoretical analysis and numerical simulation show that random waveguides and multi-path effects can bring much additional transmission loss for the noise line spectra,demonstrating the instability of ship radiated noise line spectra to a certain extent,and providing some theoretical support for advanced studies of ship radiated noise.     

准周期随机声脉冲序列信号在浅海波导中的传播

准周期随机声脉冲序列作为船舶辐射噪声信号模型具有合理性和一定普适性,这里将此模型与海洋波导结合,探讨基于此模型产生的噪声线谱经波导传播后的物理规律变化,即船舶辐射噪声经波导作用后的信号物理特性。理论分析和传播仿真计算表明,准周期声脉冲序列船舶噪声信号所含有的线谱由于受随机波导的随机性和多途干涉共同作用,序列脉冲出现的周期性显著被削弱,线谱相对幅度将\     

A sensitive method for measurements of complex third-order susceptibilities in waveguides

A method for measuring complex fast nonlinear optical nonlinearities χ ⁽³⁾ in waveguides is demonstrated. It is based on a comparison between the optical nonlinearities of two different samples under identical experimental circumstances and thus is independent of laser pulse parameters. Heterodyne detected four-wave mixing is employed to achieve information about both amplitude and phase of χ ⁽³⁾. To increase the sensitivity, a procedure for suppression of the limiting parasitic signals due to the photodiode nonlinearity is suggested. Results obtained from a short piece of hollow-core photonic bandgap fiber are presented.     

基于简化海底模型的浅海环境噪声垂直指向性及参数反演

提出了一种以简化海底模型为基础的浅海环境噪声垂直指向性的计算方法,并用于海底参数反演。小掠射角时,采用简正波法;大掠射角时,采用虚源法。数值仿真结果与经典的K/I噪声模型相近;分析某浅水区的一次噪声试验数据,提出分段反演方法,并将反演得到的参数较好的用于噪声场强度预报。结果表明,该方法引入的简化海底模型,能反映出海底反射对噪声场垂直指向性的影响,但由于不需要精确的海底分层结构,便于理论分析声场。     

无源声呐场景中使用辅助粒子滤波的邻近目标检测前跟踪方法

针对无源声呐多目标方位跟踪问题,研究了一种基于粒子滤波的检测前跟踪方法,关注于改善邻近目标和机动目标的跟踪性能。首先,提出了一种考虑了邻近目标影响的似然函数;其次,采用辅助变量利用量测信息优化粒子采样,当算法运动模型与目标实际运动状态失配时,这种策略具有很大优势。结合以上两点,提出了一种检测前跟踪算法,该算法将邻近目标划分为一组,使用邻近目标的预测状态计算目标的似然,计算效率较高。利用仿真生成的数据和海上采集的实际数据分别验证了该算法的性能,并与其他多目标粒子滤波检测前跟踪算法进行比较,证明了该算法具有良好的跟踪性能。在目标邻近和目标机动的情况下,该算法的优势更加明显。     

非刚性表面声呐目标回波的修正几何亮点模型

基于修正的Kirchhoff近似公式,本文提出了包括幅度、时延、相位跳变和局部平面波反射系数的非刚性表面声呐目标的修正四参数几何亮点模型。用原来的和修正的几何亮点模型对刚硬、裸露和敷设消声瓦的充水椭圆锥台壳体的目标强度进行了计算。结果表明原来的三参数几何亮点模型是在高频情况下未敷瓦壳体的一级近似。对于实际壳体,无论敷瓦还是未敷瓦都应采用修正的四参数几何亮点模型计算目标强度。     

A Jump-U model of echo pattern for a sonar ranging module

Sonar is extensively used in robot as a range sensor and the time-of-flight (TOF) information of ultrasonic echo is frequently adopted in sonar applications. This paper proposes a Jump-U model of ultrasonic echo pattern based on TOF data for a sonar ranging module. The model is established through a data regression method, utilizing TOF data and the relation between the delay time and the bearing angle of the sensor as input parameters. Because the proposed model can explain the jump phenomenon of TOF data and the shape of TOF data is similar to character U, the model is named as Jump-U. Moreover, the model includes several parameters, and one of them is intensity factor which can be regard as a relative strength of ultrasonic echo. Experiments are conducted to verify the proposed model by measuring the echo’s TOF data of a plane with distances ranging from 100 to 200 cm. The results show a close agreement between simulation and measurements.     

改进次最佳检测在侧扫声呐底混响抑制中的应用*

侧扫声呐进行沉底小目标探测时,底混响是主要背景干扰。底混响通常是一种非平稳、非高斯的带限噪声,它使得白噪声条件下的滤波器性能受到限制。在混响背景下常利用自回归模型对接收信号进预行白化处理,但对于实际侧扫声呐应用,白化后直接匹配滤波的处理效果不甚理想。针对此问题,在自回归模型预白化的基础上,提出采用一种次最佳检测与多分辨二分奇异值分解相结合的改进方法。该方法首先对接收信号进行分段处理,利用改进Burg算法估计每段数据自回归模型的系数及阶数;然后构造白化滤波器对分段数据预白化,并对白化后的数据进行多分辨二分奇异值分解;最后应用ostu方法对原始声图和处理后的声图进行目标检测。仿真与实验结果表明,该方法明显提高了信混比,改善了侧扫声呐沉底静态小目标的成图质量,有利于后期实现基于图像的目标自动检测。     

Simulation of low-frequency sound propagation in an irregular shallow-water waveguide with a fluid bottom

A further development of a previously proposed approach to calculating the sound field in an arbitrarily irregular ocean is presented. The approach is based on solving the first-order causal mode equations, which are equivalent to the boundary-value problem for acoustic wave equations in terms of the cross-section method. For the mode functions depending on the horizontal coordinate, additional terms are introduced in the cross-section equations to allow for the multilayer structure of the medium. A numerical solution to the causal equations is sought using the fundamental matrix equation. For the modes of the discrete spectrum and two fixed low frequencies, calculations are performed for an irregular two-layer waveguide model with fluid sediments, which is close to the actual conditions of low-frequency sound propagation in the coastal zone of the oceanic shelf. The calculated propagation loss curves are used as an example for comparison with results that can be obtained for the given waveguide model with the use of adiabatic and one-way propagation approximations.     

Selection of modes from a shallow-water noise field by single bottom hydrophones for passive tomography purposes

The possibility of selecting modes that propagate between two spaced observation points without the use of vertical arrays and low-frequency emitters is considered. Modes are selected from the cross-correlation function of noise received by single hydrophones. It is shown that modes at frequencies near the minima of the dispersion dependences of their group velocities, where stationary phase regions are observed, make the main contribution to the noise cross-correlation function. This makes it possible to identify modes of different numbers and estimate their propagation times between hydrophones, which can be the basis for shallow-water passive mode tomography using data from single bottom hydrophones. The modes were selected based on data from a experiment carried out in the Barents Sea.     

Ultraslow surface plasmons in metamaterial waveguides for subwavelength resolution

A modified planar waveguide made of a metamaterial with negative permittivity and permeability has been considered. The modification of the waveguide by the introduction of an air channel qualitatively changes its dispersion characteristics due to the appearance of an ultraslow mode. The fields and properties of this mode have been investigated. The mode has been shown to be similar to a surface plasmon. In addition, it has been shown that the plasmons can propagate in subwavelength waveguides. Such ultraslow plasmons can be used in plasmonics, microwave and accelerator techniques.     

深海海底反射区声场的相干结构及其有源声呐估距

有源声呐在探测深海海底反射区的目标时,由于声线大掠射角弯曲且声速沿声线传播路径不断变化,造成了常规估距方法产生较大的误差。有效声速法是减小常规估距方法误差的有效途径,但由于需要预先计算空间每一位置点的\     

A simple coupled mode model for near band-edge phenomena in grated waveguides

The paper presents a simple coupled mode model to describe near band-edge phenomena in the spectral response of waveguides with a section containing a rectangular grating. It is shown that nearly all relevant parameters can be determined in reasonable approximation from only the dispersion curve and one adjustable, proportionality constant. The theory is compared with results from numerical calculations and experiments.